This invention relates to medical equipment and in particular to a defibrillator having wireless communications for transferring information to and from the defibrillator in a wireless network.
One frequent consequence of heart disease is the development of cardiac arrest associated with a heart arrhythmia such as ventricular fibrillation. Ventricular fibrillation may be treated by delivering an electrical shock to the patient's heart through the use of a defibrillator. Cardiopulmonary resuscitation (CPR) is commonly used to maintain life support for victims of cardiac arrest until a defibrillator can be deployed to treat the arrhythmia.
The chances of surviving a cardiac arrest decrease rapidly over the time following the arrest. Quick response to a cardiac arrest by performing CPR and by administering a defibrillating shock is therefore of critical importance. The American Heart Association's "Chain of Survival" recites the following steps:
1. Early access to emergency care, such as by activating an emergency medical system (EMS); PA0 2. Early CPR initiated by a bystander or other first responder using basic life support (BLS) techniques to help the patient survive until more advanced care arrives; PA0 3. Early defibrillation; and PA0 4. Early advanced cardiac care. The benefits of this approach are discussed in more detail in Cummins, et al. "Improving Survival From Sudden Cardiac Arrest: the `Chain of Survival` Concept," 83 Circulation 1832-47 (May 1991).
EMS providers are playing an active role in implementing the Chain of Survival concept. Tiered EMS systems are emerging in many geographical areas and are typically divided between first responders, BLS (basic life support) providers, and ACLS (advanced cardiac life support) providers. First responders and BLS providers, often called EMT(B) or EMT-basic, the front line personnel who are first to reach a patient, are now being trained and authorized to use automatic external defibrillators (AEDs) to provide early defibrillation.
AEDs deliver a high-amplitude current impulse to the heart in order to restore normal rhythm and contractile function in the patients who are experiencing ventricular fibrillation (VF) or ventricular tachycardia (VT) that is not accompanied by a palpable pulse. AEDs differ from manual defibrillators in that AEDs can automatically analyze the electrocardiogram (ECG) rhythm to determine if defibrillation is necessary. In nearly all AED designs, the first responder is prompted to press a shock button to deliver the defibrillation shock to the patient. Paramedic defibrillators often combine the AED and manual functions into one unit to allow for use by personnel with differing levels of training.
AEDs are designed to be used primarily by first responders who may not be trained in ACLS techniques. In the pre-hospital setting, these first responders may include emergency medical technicians trained in defibrillation (EMT-Ds), police officers, flight attendants, security personnel, occupational health nurses, and firefighters. AEDs can also be used in areas of the hospital where personnel trained in ACLS are not readily available. In such cases, it may be desirable to provide a defibrillator which operates in an AED mode but with manual functions such as cardiac monitoring disabled.
In more recent AED designs such as the Heartstream Forerunner.RTM. defibrillator, the AED functions have been logically grouped into step 1, "power on"; step 2, "analyze"; and step 3, "shock." More sophisticated audio prompts have been added in addition to the visual prompts provided by the LCD display. The transition from step 1 to step 2 may be initiated by the defibrillator, such as upon detection of patient contact between the defibrillation electrodes to begin the ECG analysis as soon as possible. Proceeding from step 2 to step 3 according to the AED personality requires the user to press a shock button upon recognition of a shockable rhythm by the ECG analysis. In this way, the AED personality is commonly understood to mean semi-automatic rather than fully automatic defibrillation.
In many EMS systems, the next link in the Chain of Survival is provided with the arrival of ACLS trained paramedics equipped with full featured defibrillators/cardiac monitors ("paramedic defibrillators"). Alternatively, if no ACLS trained personnel are available, the patient is directly transported to a hospital emergency department where ACLS care can be provided. In either case, a handoff of the patient takes place between the first responder and subsequent ACLS personnel.
As part of the handoff process, medical information obtained at the scene and stored within the defibrillator must be transferred along with the patient regarding what has taken place during treatment. Commonly referred to as a code summary or an event summary, such information typically may include an ECG strip as well as markers for such events as the time of initial cardiac arrest, initiation of CPR, administration of drugs, delivery of defibrillation shocks, and so on. In addition, an audio recording ("voice strip") that documents the verbal remarks of the first responders is often provided. Such medical information contained in the event summary should be as complete and accurate as possible to ensure continuity of care and to enable the attending physician to provide the most appropriate follow-up care to the patient. It is desirable that the medical information stored in the event summary have the ability to travel alongside the patient during the various handoffs along the Chain of Survival.
The event summary may also be used by the first responder to aid in the generation of incident reports. Such incident reports often must be filed according to the requirements of the local EMS system, both for quality control and documentation. The event summary may be down-loaded or transferred to a host computer running data management software that provides for displaying, analyzing, and playing back the medical information from the event summary in a meaningful manner to reconstruct the events that took place during the emergency treatment of the patient.
Prior art defibrillators provided documentation using hard copy devices such as built-in printers to produce the ECG strip. Event markers, such as the time each defibrillation shock is administered, could be marked on the edge of the paper ECG strip. An audio recording was typically provided using a built-in audio cassette recorder. Because the ECG strip was not stored but simply printed on a paper tape, retaining a copy of the ECG strip solely for report generation was impractical.
More recent AED designs such as the Heartstream Forerunner.RTM. defibrillator record the event summary information digitally on a removable storage medium in the form of a PCMCIA memory card. A method for gathering event data is discussed in U.S. Pat. No. 5,549,115, "Method and Apparatus for Gathering Event Data Using A Removable Data Storage Medium and Clock", issued Aug. 27, 1996, to Morgan et al., and assigned to Heartstream, Inc. The information contained on the PCMCIA card is transferred by physically removing the PCMCIA card from the defibrillator and plugging it into another device such as a card reader connected to a host computer which up-loads the information to the data management software. Other AED designs provide for transferring the information via a wired connection such as an RS-232 serial link to the host computer.
Manually transferring memory cards along with the patient during a handoff from the first responder to an ACLS provider is not practical for a number of reasons. Memory cards are easily lost and may not be compatible with the defibrillator belonging to the ACLS personnel. After the handoff, the event summary stored on the memory card is then unavailable for the first responder to generate incident reports since the memory card has since been transported with patient.
Various methods for transmitting ECG information gathered remotely via telemetry back to an ECG monitor are discussed in U.S. Pat. No. 5,549,659, "Communication Interface for Transmitting and Receiving Serial Data Between Medical Instruments", U.S. Pat. No. 5,224,485, "Portable Data Acquisition Unit", and U.S. Pat. No. 5,085,224, "Portable Signaling Unit For An EKG." These methods teach sending ECG information via either hardwired or radio telemetry links for cardiac monitoring and diagnostic applications.
A method for optically coupling an ECG signal from the electrode leads to the ECG circuit is discussed in U.S. Pat. No. 4,987,902, "Apparatus for Transmitting Patient Physiological Signals" to Charles A. Couche. The opto-coupler taught by Couche provides voltage isolation between an isolated circuit such as an ECG front end and a non-isolated circuit within the medical instrument. A complex coding arrangement transforms the ECG signal into a series of pulses to avoid the use of analog to digital converters ahead of the opto-coupler in the ECG front end. However, there is no teaching by Couche to couple the ECG signal to other medical instruments or defibrillators.
ACLS personnel typically use paramedic defibrillators that contain more advanced cardiac monitoring and analysis functions such as 12 lead ECG, along with other functions such as cardiac pacing. Paramedic defibrillators generate their own event summary similar to that of AEDs and presently suffer from many of the same shortcomings as AEDs in terms of transferring medical information to and from other devices. The ECG strips that are generated by many prior art manual defibrillators are in the form of paper strips produced by a built-in printer, sometimes with annotations in the margin to mark various events during the treatment of the patient. During a handoff from ACLS personnel to the hospital emergency department, the event summary contained on the paper ECG strip is sent along with the patient, typically with no event summary information from the prior handoff from the first responder.
In an effort to reduce the number and types of defibrillators in an EMS system, it may be desirable to standardize on one type of defibrillator that may be used by both BLS and ACLS personnel. Because the training level and qualifications of BLS and ACLS personnel are different, the functions available on the defibrillator must necessarily be different. The functions may be grouped into AED functions and ACLS functions. In most cases, the AED functions are simply a subset of the ACLS functions. It is desirable that access to the ACLS functions be restricted to qualified ACLS personnel but in a way that is not overly difficult to administer by EMS personnel.
Access control to ACLS functions was accomplished in prior art defibrillators with mechanical key switches or programmable passwords entered via front panel buttons. Mechanical key switches are problematic because the key is easily lost, rendering the ACLS functions unavailable. On the other hand, the key may simply be left in the key switch for ready access in an emergency, effectively bypassing the safeguard. Similarly, passwords controlling access to ACLS functions may simply be written on the front panel of the defibrillator so that they would not have to be memorized. Thus, limiting access to the ACLS functions was difficult to administrate and quickly bypassed by personnel in the field for practical reasons.
In many EMS jurisdictions, the attending physician must be able to see the live ECG strip in real time while the patient is still in the field in order to issue orders to the EMTs to defibrillate, to administer drugs or start intravenous fluids. Such ECG strips have been typically transmitted via dedicated radio telemetry channels or cellular modems to the hospital emergency department. The defibrillator can be configured to operate as a cardiac monitor with its ECG output provided to the radio link. U.S. Pat. No. 5,593,426 "Defibrillator System Using Multiple External Defibrillators and a Communications Network", issued Jan. 14, 1997 to Morgan et al. and assigned to Heartstream, Inc. describes a communication network between multiple defibrillators and a communication station. Each defibrillator may be coupled via an infrared link to a defibrillator communicator that forms part of the communication network. However, there is no teaching by Morgan et al. of wireless communication between defibrillators.
Obtaining a live ECG strip is more often obtained by connecting an "ECG out" port on the defibrillator to either analog or digital radio telemetry channels which transmit the ECG to the attending physician. Such a communications link is very specialized, is custom tailored to work for specific equipment, and requires a connection using a data communications cable ("patch cable") to other communications equipment within the ambulance.
Defibrillators, like most types of sophisticated electronic equipment, now contain at least one microprocessor or embedded controller to perform its basic functions. Such microprocessors execute software programs stored as firmware in non-volatile memory such as read-only memory (ROM). Upgrading and maintaining the firmware is an important aspect in the manufacturing, service, and support of the defibrillator throughout its useful life. Such support typically involves the invasive activity of opening the housing of the defibrillator to physically change ROMs. In some cases, firmware upgrades could be performed with a software download from a maintenance computer via a serial port. Such activities are difficult enough to require the defibrillator be taken out of service and sent in to a central repair depot or service shop that substantially increases the overall life cycle cost of the defibrillator for the customer.
The inability to easily transfer medical information alongside the patient through the Chain of Survival has therefore been a long felt need not presently addressed by the prior art. The further inability to easily transfer information between a defibrillator and host computers for providing defibrillator service and maintenance, enabling or disabling access to ACLS functions, and training of defibrillator operators have also been long felt needs not presently addressed by the prior art. Therefore, it would be desirable to provide a wireless communication network for defibrillators using infrared data communications that allows for ready transfer of information to and from the defibrillator.